Abstract

Advances in high peak power pulse delivery in optical fibers are opposed by the intensity dependent damage threshold. The demand for high peak power therefore necessitates an increase in core diameter which often encroaches the multimode (MM) regime. Although large-mode area fibers extend the applicable power it remains ultimately limited by self-focusing with the critical self-focusing power given as P_crit = 1.86λ²/(4πn₀n₂) [1], where λ is the wavelength, n₀ the linear refractive index and n₂ the nonlinear index coefficient. For typical silica fibers P_crit ≈ 6MW at λ =1.3μm which is comparable to the 5MW peak powers of ultrashort pulses that can be obtained using Yb doped fiber amplifiers [2]. Understanding when an input pulse will self-focus to the extent that damage occurs is paramount to the design of fibers intended for high peak power pulse delivery and when selecting a design the evolution of the pulse inside the fiber must be considered and not simply the initial peak power for example.

© 2012 Optical Society of America